Electrical test devices of the aforementioned type are used to electrically contact a sample or the substrate to the electric conductors and/or components to check the operability of the substrate. The test device creates electrical connections to the substrate, on the one hand by contacting the substrate or the electrical conductors or electrical contact points of the substrate, and on the other by providing electrical contacts, which are connected to a test system, so that the test system can supply the sample with electrical signals via the test device to perform, for example, resistance measurements, current and voltage measurements or similar for a function check. Because the substrates to be tested, such as wafers, circuit boards, or solar cells, often involve extremely small components or components with a high density of electrical contact points, contact elements having small dimensions are necessary to achieve a high degree of sampling and contacting respectively on a small space. Conventionally, the guide openings in the guide plates are thereby arranged corresponding to the electrical contact points on the test sample so that the contact elements are positioned correspondingly.
Because various room and/or testing temperatures may exist when performing the test, it is necessary that thermally-caused length changes of the test device do not result in the positioning of the contact elements deviating in relation to the electrical contact points on the sample or the substrate, by means of which a test could no longer be performed successfully. It is therefore known to provide centering devices, which permit a temperature expansion leeway in the test device in such a manner that an offset of the contact elements due to temperature-contingent quantity changes are minimal.
In this regard, patent application DE 10 2004 023 987 A1 for example reveals an electrical test device with a centering device, which permits only a radial, in other words leading towards or away from the center, temperature margin in relation to the center of the test device or the contact head, in other words the center in a plane parallel to the guide plates. By the radial orientation toward the center, one achieves an overall minimum shift in case of temperature-contingent quantity changes because the length changes in the respective plate cannot have a cumulative effect over the entire width of the respective guide plate.
To do so, the centering device has multiple centering pins, which are attached to the spacer in centering openings and are inserted in the slots in the guide plates, wherein the longitudinal direction of the slots is oriented radially toward the center. To ensure proper operation, high tolerance requirements are thereby to be fulfilled by the centering pins, slots, and centering openings. The centering openings are thereby designed as boreholes, in other words with a circular contour, which is why high requirements are placed on the manufacturing tolerances to permanently ensure a functioning centering operation.